Factory replacement cases were blank with the intention that the dealer would stamp in the number of the old cases being replaced. It did not always happen. I have several sets of blank cases. Depending on your local it may or may-not matter. Some places want both an engine number and frame VIN. Some don't care. Just be sure before you jump in ! And ALL factory built bikes had numbers on the cases, from the beginning of time!
Robbie
Robbie